A current networking trend is to provide “IP all the way” to wired and wireless units. Some objectives are to simplify the infrastructure, to support a wide range of applications, and to support diverse user demands on the communication service. A consequence of this is that the heterogeneity of the IP networks increases, both from a business perspective and from a technical perspective. From a business perspective, some providers offer services for particular application segments without having their own network infrastructure. Instead they operate overlay networks by acquiring transmission capacity from IP network providers. An overlay network is a logical layer four service network running on top of a real IP network. From a technical perspective, having IP as the general-purpose network layer, the range of used link layer technologies is increased.
A design trade-off made to enable interconnection was to support only best-effort service at the network level. Best-effort service provides adequate support for traditional data applications that can tolerate delay, loss and varying throughput along the path. However, in networks carrying high loads of traffic, this type of service is often inadequate for meeting the demands of applications that are more sensitive to packet loss and delay e.g. telephony, video on demand, multimedia conferencing, etc. It is also insufficient to separate the services for priority businesses.
One trend is to simplify the infrastructure by running all kinds of applications and support all kinds of customers, with various network service demands, in the same logical IP network i.e. the Internet. This means that IP becomes the unifying communication technology i.e., the network layer. Consequently the environment in which IP must operate becomes more heterogeneous in the following aspects: the application heterogeneity in IP networks is increasing, the link layer heterogeneity is increasing, including Asynchronous Transfer Mode (ATM), Multiprotocol Label Switching (MPLS), Local Area Network (LAN), Virtual LAN (VLAN), Wireless LAN (WLAN), Global Service Mobile (GSM), Universal Mobile Telephony System (UMTS), etc, the user community is becoming more heterogeneous in terms of service expectations and willingness to pay for the service e.g. professional users and home entertainment users, and the business range is becoming more diverse including a mixture of network providers and service providers that specialise on different overlay services and peer-to-peer applications.
All these trends point towards the Internet becoming a ubiquitous multi-service network. Consequently, there are strong commercial reasons for service providers, network operators and equipment providers to offer unified solutions for ensured Quality-of-Service (QoS) in IP networks.
There are several challenges in providing end-to-end services over an IP network spanning various kinds of link layer technologies: a) IP routers and link layer switching devices should be kept simple and not be burdened with additional processing or signalling functionality. b) The link layers may have a vast range of build-in functionality for service management that should be interfaced e.g., ATM and 3G wireless has plenty of functionality, while LAN and WLAN has very little. c) The services must be able to manage in a uniform way by the network operators, both at IP level and inside particular link-layer networks. d) The services must be transitively ensured in a hierarchy of business overlays as well as over a chain of peer providers co-operating to offer particular services.
The entity performing dynamic service management in a provisioned network is here called a Network Resource Manager (NRM) (other commonly used terms for this entity are bandwidth broker, bandwidth manager, network resource controller, network agent, etc.). This entity keeps track of available resources and performs admission control on incoming requests for resources from clients. To perform admission control the NRM stores a history of previously admitted resource reservations. The NRM manager takes decisions to admit new requests for resources based on the total amount of available resources, the amount currently reserved by previously reservations and the amount of resources requested. The resources may or may not be scheduled over time.
There are specific requirements for resource management mechanisms. To provide service to end users, they must be aware of network resources and may schedule them for the committed service at any granularity e.g. for a port range, for aggregate traffic between a pair of subnets, etc. There are currently very few known specifications and implementations of NRMs. Only some of them handle reservations involving multiple domains, i.e. inter-domain reservations between peering network operators. These are described below. None of them handle the heterogeneous and hierarchical aspects of specific link-layers and overlay networks.
In Olov Schelén, “Quality of Service Agents in the Internet”, Doctoral Thesis, Department of Computer Science and Electrical Engineering, Division of Computer Communication, Luleå University of Technology, Luleå, 1998 an NRM is described that handles resource management on the IP-level, intra-domain and inter-domain, through peering. It includes IP topology awareness, admission control, resource scheduling over time and aggregation towards destination domains. It is a pure IP network layer solution that does not handle specific link layer solutions or hierarchies of service providers.
P. Pan, E. Hahne, and H. Schulzrinne have developed a protocol called Border Gateway Resource Protocol (BGRP). They aggregate reservations with the same destination in the border router in the source domain. This solution is focused on IP-level inter-domain resource management for IP network operators, running Border Gateway Protocol (BGP).
The QBone Signaling workgroup has specified a protocol for inter-domain QoS signalling called SIBBS. The concept relies on signalling each reservation request hop by hop between instances of NRMs. End-to-end admission control is provided with some limited aggregation. In V. Sander et al, “End-to-End Provision of Policy Information for Network QoS”, The University of Chicago, inter-domain reservations and signalling between different resource managers are discussed and two models of signalling is primarily discussed.
There are a number of projects that have designed architectures for service management. One of these projects is Cadenus [IST Cadenus: Creation and Deployment of End-User Services in Premium IP networks]. In the Cadenus model, disclosed in O. Dugeon, A. Diakonescu: “From SLA to SLS up to QoS control: The CADENUS Framework”, WTC'2002, http://www.cadenus.org/papers, there are units for access mediation, service mediation, resource mediation, and network control. The Resource Mediation component resembles what is denoted as NRM in this specification.
Drafts disclosed in IETF Next Step In Signaling (NSIS) working group: http://www.ietf.org are primarily focused on path-coupled signalling hop-by-hop between signalling aware routers. One proposal, named CASP, is claimed to provide also path-decoupled signalling that possibly could be used between instances of NRMs.
For RSVP-based signalling, which is router centric and stateful, there has been a proposal for a Subnet Bandwidth Manager (SBM) to handle resource management in one specific link layer technology known as 802.x LANs described in R. Yavatkar et al. “SBM (Subnet Bandwidth Manager): A Protocol for RSVP-based Admission Control over IEEE 802-style networks”. IETF. RFC 2814.
The technologies described above, except SBM and CADENUS, focus on resource management at the IP network layer only. All proposals are quite static in supporting hierarchical resource management for specific link-layers. In the case of Cadenus, there is a technology dependent Network Controller that can handle particular link-layer technologies. In the case of SBM, it acts as a black-box admission controller for RSVP like signalling to provide admission control inside a particular kind of link layer network. This provides a solution only for IEEE 802 link layer technologies.
Thus the proposed solutions provide either single level IP resource management or strict link-level resource management. This means that none of these solutions provide uniform resource management for the unifying communication technology that IP network layer has become i.e., including various applications and overlay networks as well as different link layer technologies. More specifically, the proposed solutions have the following drawbacks:                None of the proposed solutions provide uniform service management for hierarchies of customers and providers i.e., overlay network service providers, Virtual Private Networks (VPNs), Enterprises, etc. being customers to different networks operators.        They do not provide a general model for handling resources in hierarchies of link layer solutions, allowing some solutions to use internal support for resource management and providing other solutions with full support for network resource management at particular sub-levels of IP.        Service management is complicated from an operator's point of view because separate tools/views are needed to manage different link layer technologies.        End-to-end services can not be provided effectively because the admission control architecture does not connect IP network layer resources and link layers specific resources seamlessly.        No automated services through self management by customers can be offered since there is no unified solution for service invocation over the different protocol layers i.e., the IP network layer and underlying link layers.        
In addition to the above mentioned drawbacks, the proposed solutions have the following limitations:                Network operators obtain little feedback on the booking levels, currently and over time, in networks and sub-networks since the proposed solutions do not support synchronized and unified scheduling of resources at both these layers.        For link layer management, current solutions do no clearly separate the functions for sub-network control such as control of a domain with devices and functions for device control such as control of specific devices. Consequently, adding support for new devices is cumbersome since that may affect the functions for sub-network control.        